1. Field of the Invention
The present invention relates to an inlet screen assembly for the inlet of a pump for pumping liquids. More particularly, the present invention relates to a tubular inlet screen assembly that is adapted to be received over a tubular pump suction inlet, through which inlet flow of a liquid into the pump takes place in a generally radial direction relative to the pump suction tube axis.
2. Description of the Related Art
Inlet screens or filters of various forms are frequently utilized to prevent the entry through the inlet of a liquid pump of particulate matter that could enter into the interior of the pump and possible cause internal damage. For example, in submersible pumps that are utilized to pump liquids from a borehole in the ground, screens are provided at the pump suction inlet to block the entry of large particles of rock or other hard materials into the interior of the pump. Such screens have openings that have a size that is selected based upon the smallest size particles that are to be blocked from entering the pump housing. Some pumps include screens that are fixed to the pump inlet by the pump manufacturer. Oftentimes pump inlet screens are designed and constructed to fit only a given size pump inlet structure, thereby requiring a different screen component for each pump.
Particulate-blocking-screens are especially necessary to protect the interior components of submersible pumps that are utilized in pumping underground water or other submerged liquids. One common application of a submersible pump is in connection with the pumping of water from underground coal bed methane gas wells. In that regard, underground coal seams are often saturated with water, and the pressure of the water operates to confine the methane gas within the coal seam and hampers its recovery. Accordingly, submersible liquid pumps are needed to pump large volumes of water from below the ground to release the water pressure that traps the methane gas within the coal seam, and thereby facilitate the recovery of the trapped methane gas. Typically, submersible pumps operating in such wells have multiple, sequentially arranged impellers and can pump from about 5 to about 20 gallons of water per minute. And as the subterranean water pressure is reduced as a result of the removal of water from the well, the methane gas is liberated and migrates toward the well bore, where it can be collected and brought to the surface.
In operating submersible pumps in underground coal bed methane wells, it is necessary to provide screens over the pump inlets in order to prevent the entry into the pump of abrasive materials, such as rock and coal particles. Because of their hardness, such particles can cause rapid wear of the pump internal parts, including the impellers and shaft bearings, and they can also degrade the effectiveness of internal seals. As a result, the pump operating efficiency is reduced and removal and replacement of the entire pump is required to maintain the desired pumping rate, or, alternatively, the removal and repair of the pump, in either case resulting in undesirable pump and well downtime. In that regard, commonly utilized screen structures for such submersible pumps generally are in the form of punched plates having circular openings of a size to prevent the entry into the pump interior of rock or coal particles that are greater than a predetermined size and that could cause damage to, such parts as the pump impeller. However, such punched plates often limit the pump flow rate because the circular opening pattern provides a relatively small open area of the overall plate surface. Additionally, such punched plate inlet screen structures are commonly affixed to the pump structure by the pump manufacturer, such as by the use of pop rivets, or the like, and are therefore not interchangeable or adapted to fit other pump suction tube sizes.
There is therefore a need for an pump inlet screen structure for a submersible pump to block the entry into the pump housing of smaller size particles, without unnecessarily restricting pump flow, and that is easily removable and replaceable, and that also is so configured that it can be utilized on pumps having somewhat different suction tube diameters.